1. Field of the Invention
The present invention relates to radiation generating apparatuses for, in particular, diagnostic application in the field of medical equipment and nondestructive radiography in the field of industrial equipment.
2. Description of the Related Art
Radiation generating apparatuses that generate X-rays for use in medical diagnosis and industrial non-destructive imaging are required to have a high durability and maintenance efficiency to increase the operating rate thereof. Such a radiation generating apparatus may serve as a portable medical modality applicable to home medical care or emergency medical care in case of, for example, a disaster or an accident.
The thermal stability of a target that serves as a source of radiation is one of the main factors that determine the durability of the radiation generating apparatus.
In the radiation generating apparatus, which generates radiation by irradiating the target with electron beams, the “radiation generation efficiency” of the target is less than 1% because most of the energy supplied by the electron beams to the target is converted into heat. When dissipation of the heat generated by the target is not sufficient, a problem occurs in that the adhesion of the target to its support member is reduced due to thermal stress, and the thermal stability of the target is limited.
A known method for increasing the “radiation generation efficiency” of the target is to use a transmissive target including a thin-film-shaped target layer, which contains a heavy metal, and a support member, which allows the radiation to pass therethrough and supports the target layer. PCT Japanese Translation Patent Publication No. 2009-545840 discloses a rotating-anode transmissive target with which the “radiation generation efficiency” is increased to 1.5 times that of a known rotating-anode reflective target.
A known method for promoting the dissipation of heat from the target to the outside is to use diamond as the material of the support member that supports the target layer of the multilayer target. U.S. Pat. No. 6,850,598 discloses that the heat dissipation effect can be increased and the focal spot size can be reduced when the support member that supports the target layer, which is made of tungsten, is made of diamond. Diamond has high radiotransparency as well as high thermal stability and thermal conductivity, and is therefore suitable as a material of a support member of a transmissive target.
With the development of image processing technologies, such as tomography, for medical diagnosis, array-type radiation generating apparatuses that emit a plurality of X-ray beams have been developed as a modality. Such an array-type radiation generating apparatus includes radiation generating units arranged in an array, and each radiation generating unit is configured to be individually controllable.
Japanese Patent Laid-Open No. 2007-265981 discloses a structure of an array-type radiation generating apparatus in which shielding members having openings are provided on front and back sides of a plate-shaped target including a plurality of radiation generating units. The plate-shaped target is thermally in contact with the shielding members. Owing to this structure, according to Japanese Patent Laid-Open No. 2007-265981, a plurality of X-ray beams with regulated radiation angles are emitted toward the front of the radiation generating apparatus, and the heat of the target can be radiated through the shielding member on the front side of the target.